Halofluorination of alkenes using trihaloisocyanuric acids and HF-pyridine

Article abstract of DOI:10.1055/s-0029-1220011

Halofluorination of alkenes with a new system (trihaloisocyanuric acids and HF-pyridine) results in the formation of vicinal halofluoroalkanes. The reaction is regioselective leading to Markovnikov-oriented products and the halofluorinated adducts follow anti-addition in the case of cyclohexene and 1-methylcyclohexene. Reaction yields range from 67-88%. Georg Thieme Verlag Stuttgart · New York.

Full text of DOI:10.1055/s-0029-1220011

PAPER
2379
Halofluorination of Alkenes Using Trihaloisocyanuric Acids and HF⋅Pyridine
H
alofluorination
í
of Al
v
kenes ia T. C. Crespo, Rodrigo da S. Ribeiro, Marcio C. S. de Mattos,* Pierre M. Esteves*
Instituto de Química, Departamento de Química Orgânica, Universidade Federal do Rio de Janeiro, Cx Postal 68545, 21945-970,
Rio de Janeiro, Brazil
Fax +55(21)25627256; E-mail: pesteves@iq.ufrj.br; E-mail: mmattos@iq.ufrj.br
Received 29 January 2010; revised 8 April 2010
In memory of Prof. Octavio Augusto Ceva Antunes
oxone®,7b and triiodoisocyanuric acid (TICA) is synthe-
Abstract: Halofluorination of alkenes with a new system (triha-
sized from TCCA and I2 in a sealed tube.8a These triha-
loisocyanuric acids and HF·pyridine) results in the formation of vic-
loisocyanuric acids are very interesting from a green
inal halofluoroalkanes. The reaction is regioselective leading to
Markovnikov-oriented products and the halofluorinated adducts
chemistry point of view, as they are easily handled stable
follow anti-addition in the case of cyclohexene and 1-methylcyclo- solids and also present a good atom economy9 as they can
hexene. Reaction yields range from 67–88%.
transfer most part of their mass to the substrate (Table 1).
Furthermore, in these reactions, cyanuric acid precipitates
as a by-product, which can be recovered by filtration and
reused to prepare more trihaloisocyanuric acid.10
Key words: electrophilic addition, halogenation, alkenes, halides,
regioselectivity
Table 1 Atom Economy of N-Halo Compoundsa
Organofluorine compounds show interesting chemical
and physical properties and biological activities, raising
interest in many fields.1 The introduction of fluorine into
organic compounds increases thermal and oxidative sta-
bility, alters electronic effects and lipophilicity, and also
closely mimics hydrogen and oxygen in steric require-
ments.2 Organofluorine compounds have been used as lu-
bricants, coatings for cooking utensils, propellants,
refrigerants, solvents, dyes, liquid crystals, surfactants, in
the production of agrochemicals, and in pharmaceutical
industry.2a,3
X
Cl
Br
I
TXCA
45.5
65
NXS
26.4
45
NXSac
16.3
30.5
75
56.5
41.1
a Active halogen content (w/w%) that can be transferred to the prod-
uct.
In this work, we describe a new methodology for the regio-
selective halofluorination of alkenes using Olah’s reagent
as the source of fluorine and TXCA as the source of elec-
trophilic halogen.
An important method to place fluorine into organic mole-
cules is the halofluorination of unsaturated compounds4
and several protocols have been developed. The 70%
HF·pyridine (Olah’s reagent) or Et3N·HF are most com-
monly used as fluoride sources, and N-halosuccinimide
(NXS) or N-halosaccharin (NXSac) as sources of electro-
philic halogen.5 Trihaloisocyanuric acids (TXCA,
Figure 1) have been recently shown to be efficient haloge-
nating agents, due to their capability of halonium (‘X+’)
atom transfer to unsaturated substrates.6–8
Initially, the bromofluorination of styrene using tribro-
moisocyanuric acid and Olah’s reagent in different condi-
Table 2 Bromofluorination Reaction of Styrene with Tribromoiso-
cyanuric Acid and Olah’s Reagent
F
Br
HF⋅Py, TBCA (0.68 mmol)
Trichloroisocyanuric acid (TCCA) is a stable and inex-
pensive solid frequently used for swimming pool disinfec-
tion and is easily available in pool supply and in some
hardware stores.6 Tribromoisocyanuric acid (TBCA) is
easily and safely prepared from cyanuric acid, KBr, and
solvent
(2 mmol)
Ratio styrene–HF· Time
Temp
Solvent
Conv.
(%)a
Py–TBCA
1:10:0.34
1:10:0.34
1:10:0.34
1:10:0.34
1:2:0.34
(min)
X
20
r.t.
THF
41b
31c
O
X
N
O
X
X = Cl (TCCA)
X = Br (TBCA)
X = I (TICA)
30
r.t.
MeCN
CH2Cl2
CH2Cl2
CH2Cl2
N
N
20
r.t.
100
100
100
O
30
–10 °C
r.t.
Figure 1 Trihaloisocyanuric acids
180
SYNTHESIS 2010, No. 14, pp 2379–2382
Advanced online publication: 18.05.2010
DOI: 10.1055/s-0029-1220011; Art ID: M00810SS
© Georg Thieme Verlag Stuttgart · New York
x
x.
x
x
.
2
0
1
0
a Determined by HRGC-MS.
b Formed along with two unidentified products.
c Formed along with incorporation of MeCN to the substrate.

2380
L T. C. Crespo et al.
PAPER
tions was evaluated (Table 2). It was observed that methane was also evaluated and the results are shown in
dichloromethane is the best solvent for halofluorination Table 3.
reaction in HF·Py/TBCA system. The HF·Py/TBCA mo-
The reactions leads selectively to products according to
lar ratio of 6 in dichloromethane is enough for the com-
Markovnikov’s rule. Cyclohexene and 1-methylcyclohex-
plete conversion of the substrate, leading to the
ene afford halofluorinated adducts, explained by an anti-
addition. The trans-stereochemistry of the halofluorina-
corresponding bromofluorinated product. The main dif-
ference in such reactions is the reaction time, which de-
tion adducts indicates the formation of a halonium ion as
creases with the increase of the HF·Py/TBCA molar ratio.
reaction intermediate, which is further attacked by a fluo-
Based on the above results, the halofluorination of several ride ion (Scheme 1).
alkenes (styrene, a-methylstyrene, cyclohexene, and 1-
methylcyclohexene) using the trihaloisocyanuric acids
(0.34 mol equiv) and HF·Py (2 mol equiv) in dichloro-
O
X
X
O
X
X
N
N
δ+
δ–
N
N
HF⋅Py
O
X
N
+
CH2Cl2
O
N
X
O
Table 3 Halofluorination of Alkenes with Trihaloisocyanuric Acids
O
R1
F
X
R1
R2
HF⋅Py, TXCA
CH2Cl2, r.t.
R2
R3
R3
F–
Alkene
Time (h) Product
Yield (%)
79
X
F
X
+
F
F
F
X
Br
3
Scheme 1 Reaction intermediates for halofluorination of alkenes
with trihaloisocyanuric acids
I
21
83
The reactions lead to pure products in most cases in good
yields. The yields are comparable with the HF·Py/NXS or
HF·Py/NXSac systems for cyclohexenes, but consider-
ably higher for styrenes (Table 4). However, despite the
yields, TXCA proved to be more convenient than other N-
halo compounds in halofluorination reactions for both
easy handling and, especially, their higher atom econo-
my,9 as shown in Table 1.
80a
85
Cl
Br
I
0.5
3
F
F
F
Table 4 Comparison of Yields for Halofluorination Reactions
R1
F
X
R1
R2
N-halo compound
2
77
R2
R3
R3
HF⋅Py
R1
H
R2
R3
X
Br
I
TXCA NXS
NXSac
70b
-(CH2)4-
-(CH2)4-
-(CH2)4-
H
88
75
86
80
79
85
905b
755b
–
–
Cl
0.5
H
–
Me
Ph
Ph
Ph
I
895n
505j
–
F
19
15
7
88
75
67
86
H
H
H
Cl
Br
Br
–
Br
F
H
535p
725p
Me
–
I
F
The formation of chloroalkenes in the chlorofluorination
reaction of styrene and a-methylstyrene suggest the exist-
ence of a b-chlorinated carbocation intermediate, which
can be deprotonated affording the corresponding allyl or
vinyl chlorides11 (Scheme 2). The result of cis and trans
products obtained by Dolenc and Sket5j in the reaction of
indene with N-chlorosaccharin/HF·Py is also an evidence
against the involvement of a chloronium ion as an inter-
Br
F
I
7
a Formed along with b-chlorostyrene (20%).
b Formed along with b-chloro-a-methylstyrene and a-(chlorometh-
yl)styrene (30%).
Synthesis 2010, No. 14, 2379–2382 © Thieme Stuttgart · New York

PAPER
Halofluorination of Alkenes
2381
13C NMR (50 MHz, CDCl3): d = 34.4 (CH2, d, J = 28.4 Hz), 92.8
(CH, d, J = 178.0 Hz), 125.8 (2 CH, d, J = 6.8 Hz), 128.8 (2 CH, s),
129.3 (CH, s), 137.2 (C, d, J = 20.3 Hz).
19F NMR (282 MHz, CDCl3): d = –174.7 (m).
O
Cl
Cl
O
Cl
Cl
O
N
N
δ+
Cl
δ–
HF⋅Py
CH2Cl2
N
N
+
O
N
O
N
R
Ph
O
MS: m/z (%) = 202 and 204 [M+ and (M + 2)+, 7], 122 (3), 109 (100),
Cl
103 (8), 77 (11), 51 (14).
F–
Cl
b
1-Bromo-2-fluoro-2-phenylpropane5l
Yellowish liquid, after purification by preparative chromatography
on SiO2 using hexane as eluent.
1H NMR (200 MHz, CDCl3): d = 1.8 (d, J = 22.0 Hz, 3 H), 3.5–3.7
(m, 2 H), 7.4 (m, 5 H).
13C NMR (50 MHz, CDCl3): d = 25.6 (CH3, d, J = 24.4 Hz), 40.6
(CH2, d, J = 28.4 Hz), 95.0 (C, d, J = 178.6 Hz), 124.6 (2 CH, d,
J = 9.1 Hz), 128.4 (CH), 128.7 (2 CH), 141.8 (C, d, J = 21.8 Hz).
b
H
b
Cl
Ph
a
H
a
Ph
F–
Cl
Cl
Ph
F
Ph
Scheme 2 Reaction intermediates for chlorofluorination of styrene
with trichloroisocyanuric acid
19F NMR (282 MHz, CDCl3): d = –148.0 (quint d, J = 22.1, 16.8
Hz).
MS: m/z (%) = 216 and 218 [(M+ and (M + 2)+, 5], 196 (2), 123
(100), 103 (31), 77 (14), 51 (14).
mediate in the chlorofluoration reactions with styryl sys-
tems.
trans-1-Bromo-2-fluorocyclohexane5b
Yellowish liquid, after purification by preparative chromatography
on SiO2 using EtOAc–hexane (20%) as eluent.
1H NMR (200 MHz, CDCl3): d = 1.2–2.0 (m, 6 H), 2.0–2.4 (m, 2
H), 3.9–4.1 (m, 1 H), 4.3–4.7 (dtd, J = 48.3, 8.4, 4.3 Hz, 1 H).
13C NMR (50 MHz, CDCl3): d = 22.8 (CH2, d, J = 8.7 Hz), 25.0
(CH2), 31.2 (CH2, d, J = 19.1 Hz), 34.8 (CH2, d, J = 3.7 Hz), 52.5
(CH, d, J = 19.8 Hz), 94.0 (CH, d, J = 179.2 Hz).
In conclusion, the present work describes the use of triha-
loisocyanuric acids as an efficient halogenating reagent
for halofluorination reaction of alkenes. These reagents
are inexpensive, readily prepared, easy-to-handle solids,
safe, and more useful in terms of atom economy than the
traditional reagents used in halofluorination reaction. Re-
action yields range from 67–88%.
19F NMR (282 MHz, CDCl3): d = –168.1 (dm, J = 44.9 Hz).
MS: m/z = 180 and 182 [M+ and (M + 2)+, 2], 101 (31), 81 (100), 72
Alkenes (Aldrich), Olah’s reagent (Alfa Aesar), and TCCA (Acros
Organics) were used as received. TBCA7b and TICA8a were pre-
pared according to published procedures. NMR spectra were re-
corded on a Bruker AC-200 spectrometer at 300 MHz (1H) and at
75 MHz (13C) in CDCl3 with TMS as internal standard. 19F NMR
spectra were recorded in a Bruker DRX-300 spectrometer at 282
MHz in CDCl3 (fluorobenzene as reference). HRGC-MS analyses
were performed on a Shimadzu GCMS-QP2010S gas chromato-
graph with electron impact (70 eV) by using a 30 m DB-5 silica cap-
illary column. All reactions were performed using a single-necked
high density PTFE flask under argon and were monitored by
HRGC. After workup, the solvent was evaporated on a rotatory
evaporator at reduced pressure and controlled heating or carefully
distilled. Whenever necessary, the product was purified using a
20 × 20 cm SiO2 preparative plate.
(8), 59 (24).
trans-2-Bromo-1-fluoro-1-methylcyclohexane5k
Yellowish liquid, after purification by preparative chromatography
on SiO2 using EtOAc–hexane (20%) as eluent.
1H NMR (200 MHz, CDCl3): d = 1.5–1.6 (d, J = 22.5 Hz, 3 H), 1.4–
2.3 (m, 8 H), 4.2 (td, J = 7.4, 3.9 Hz).
13C NMR (50 MHz, CDCl3): d = 22.1 (CH2, d, J = 6.3 Hz), 22.9
(CH2), 23.8 (CH3, d, J = 24.6 Hz), 33.2 (CH2), 34.8 (CH2, d,
J = 17.5 Hz), 57.2 (CH, d, J = 26.3 Hz), 95.6 (C, d, J = 172.6 Hz).
19F NMR (282 MHz, CDCl3): d = –137.3 (m).
MS: m/z (%) = 194 and 196 [M+ and (M + 2)+, 1], 134 (2), 132 (2),
115 (11), 99 (5), 95 (100), 73 (49).
Halofluorination of Alkenes with HF·Py/TBCA System; Gener-
al Procedure
2-Chloro-1-fluoro-1-phenylethane5j
Yellowish liquid, after purification by preparative chromatography
on SiO2 using hexane as eluent.
1H NMR (200 MHz, CDCl3): d = 3.6–3.9 (m, 2 H), 5.4–5.7 (dm,
J = 47.1, 6.0, 4.3 Hz, 1 H), 7.4 (s, 5 H).
13C NMR (50 MHz, CDCl3): d = 47.1 (CH2, d, J = 28.2 Hz), 93.3
(CH, d, J = 178.2 Hz), 126.0 (2 CH, d, J = 6.8 Hz), 128.9 (2 CH),
129.5 (CH, d, J = 1.5 Hz), 136.8 (C, d, J = 20.0 Hz).
A magnetically stirred mixture of the alkene (2 mmol) and 70%
HF·Py (4 mmol) in anhyd CH2Cl2 (10 mL) contained in a 50 mL,
single-necked PTFE flask equipped with a septum and under argon,
was treated with trihaloisocyanuric acid (0.68 mmol) at 0 °C. After
the addition, the ice bath was removed, and the stirring continued at
r.t. After completion (Table 3), the reaction was quenched with dis-
tilled H2O (10 mL), and the product was extracted with CH2Cl2
(3 × 10 mL). The combined organic layers were subsequently
washed with sat. aq NaHCO3 (10 mL) and dried (Na2SO4). After fil-
tration and evaporation of the solvent, the product was character-
ized by standard analytical techniques (Table 3).
19F NMR (282 MHz, CDCl3): d = –179.1 (ddd, J = 15.9, 25.5, 46.9
Hz).
MS: m/z (%) = 158 and 160 [M+ and (M + 2)+, 10.9, 3.5], 140 (1.5),
138 (7), 109 (100), 103 (15), 77 (11), 51 (16).
2-Bromo-1-fluoro-1-phenylethane5k
Colorless liquid.
1-Chloro-2-fluoro-2-phenylpropane5m
Yellowish liquid, after purification by preparative chromatography
1H NMR (200 MHz, CDCl3): d = 3.5–3.7 (m, 2 H), 5.5–5.8 (ddd,
J = 46.9, 7.0, 4.6 Hz, 1 H), 7.4 (m, 5 H).
on SiO2 using hexane as eluent.
Synthesis 2010, No. 14, 2379–2382 © Thieme Stuttgart · New York

2382
L T. C. Crespo et al.
PAPER
1H NMR (200 MHz, CDCl3): d = 1.8 (d, J = 22.2 Hz), 3.7–3.9 (m,
2 H), 7.4 (s, 5 H).
Acknowledgment
We thank CNPq and FAPERJ for financial support and Prof. Rosa-
ne San Gil for 19F NMR analysis.
13C NMR (50 MHz, CDCl3): d = 24.5 (CH3, d, J = 24.4 Hz), 51.8
(CH2, d, J = 28.4 Hz), 95.8 (C, d, J = 178.5 Hz), 124.7 (2 CH, d,
J = 9.1 Hz), 128.4 (2 CH), 128.7 (CH), 141.7 (C, d, J = 21.6 Hz).
19F NMR (282 MHz, CDCl3): d = –150.9 (quint d, J = 16.4, 22.1
Hz).
References
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1-Fluoro-2-iodo-1-phenylethane5l
Yellowish liquid.
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J = 46.7, 7.3 Hz, 1 H), 7.4 (m, 5 H).
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(CH, d, J = 177.5 Hz), 125.70 (2 CH, d, J = 6.5 Hz), 128.80 (2 CH),
129.20 (CH), 138.05 (C, d, J = 20.5 Hz).
19F NMR (282 MHz, CDCl3): d = –167.10 (ddd, J = 40.8, 24.2, 16.6
Hz).
MS: m/z (%) = 250 (M+, 2), 230 (3), 123 (100), 109 (32), 103 (62),
77 (35), 51 (21).
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2-Fluoro-1-iodo-2-phenylpropane5l
Yellowish liquid.
1H NMR (200 MHz, CDCl3): d = 1.9 (d, J = 21.8 Hz, 3 H), 3.6 (d,
J = 20.3 Hz, 2 H), 7.4 (m, 5 H).
13C NMR (50 MHz, CDCl3): d = 15.7 (CH3, d, J = 28.2 Hz), 27.1
(CH2, d, J = 24.5 Hz), 94.6 (C, d, J = 178.5 Hz), 124.4 (2 CH, d,
J = 9.1 Hz), 128.3 (2 CH), 128.7 (CH), 141.9 (C, d, J = 22.0 Hz).
19F NMR (282 MHz, CDCl3): d = –142.6 (sext, J = 21.0 Hz).
MS: m/z (%) = 264 (M+, 2), 244 (4), 137 (100), 123 (43), 103 (30),
77 (24), 51 (32).
trans-2-Fluoro-1-iodocyclohexane5b
Yellowish liquid, after purification by preparative chromatography
on SiO2 using EtOAc–hexane (20%) as eluent.
1H NMR (200 MHz, CDCl3): d = 1.3–1.6 (m, 4 H), 1.6–2.0 (m, 2
H), 2.0–2.5 (m, 2 H), 4.0–4.2 (m, 1 H), 4.4–4.7 (dtd, J = 47.7, 8.6,
4.1 Hz, 1 H).
13C NMR (50 MHz, CDCl3): d = 23.0 (CH2, d, J = 8.6 Hz), 26.3
(CH2), 30.9 (CH2, d, J = 18.8 Hz), 31.4 (CH, d, J = 19.5 Hz), 36.6
(CH2, d, J = 3.7 Hz), 94.8 (CH, d, J = 179.4 Hz).
19F NMR (282 MHz, CDCl3): d = –160.0 (dm, J = 40.0 Hz).
MS: m/z (%) = 228 (M+, 14), 127 (6), 101 (33), 81 (100), 59 (33).
trans-1-Fluoro-2-iodo-1-methylcyclohexane5l
Yellowish liquid, after purification by preparative chromatography
on SiO2 using EtOAc–hexane (20%) as eluent.
1H NMR (200 MHz, CDCl3): d = 1.3–1.6 (d, J = 22.4 Hz, 3 H), 1.3–
2.3 (m, 8 H), 4.4 (td, J = 7.8, 3.9 Hz, 1 H).
13C NMR (50 MHz, CDCl3): d = 22.4 (CH2, d, J = 6.7 Hz), 25.0
(CH2), 25.9 (CH3, d, J = 24.4 Hz), 34.8 (CH2, d, J = 21.2 Hz), 35.6
(CH2, d, J = 4.5 Hz), 38.4 (CH, d, J = 23.3 Hz), 95.4 (C, d, J = 173.6
Hz).
19F NMR (282 MHz, CDCl3): d = –132.6 (dm, J = 93.0 Hz).
MS: m/z (%) = 242 (M+, 3), 115 (18), 95 (100), 73 (34).
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Synthesis 2010, No. 14, 2379–2382 © Thieme Stuttgart · New York